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Search Results: 1 - 10 of 401245 matches for " M. Zebarjad "
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Excited states energy corrections of hydrogen atom at the order of & alpha4 using NRQED as an effective field theory
S. M. Zebarjad,M. Bigdeli
Iranian Journal of Physics Research , 2003,
Abstract: In this paper, we calculate Hydrogen hyperfine splitting (HFS) at the order a4 by using NRQED as an effective field theory. We also show the leading-order contribution of nuclear size to the energy correction of Hydrogen atom .
Positronium Hyperfine Splitting in Non-commutative Space at the Order $α^6$
M. Haghighat,S. M. Zebarjad,F. Loran
Physics , 2001, DOI: 10.1103/PhysRevD.66.016005
Abstract: We obtain positronium Hyperfine Splitting owing to the non-commutativity of space and show that, in the leading order, it is proportional to $\theta \alpha^6$ where, $\theta$ is the parameter of non-commutativity. It is also shown that spatial non-commutativity splits the spacing between $n=2$ triplet excited levels $E(2^3S_1)\to E(2^3P_2)$ which provides an experimental test on the non-commutativity of space.
A Study on Mechanical Properties of PMMA/Hydroxyapatite Nanocomposite  [PDF]
S. M. Zebarjad, S. A Sajjadi, T. Ebrahimi Sdrabadi, S. A Sajjadi, A Yaghmaei, B Naderi
Engineering (ENG) , 2011, DOI: 10.4236/eng.2011.38096
Abstract: This study is focused on the role of nano hydroxyapatite particles on the mechanical properties of PMMA/HA nanocomposites. In order to achieve a proper and homogeneous distribution of HA particles in the polymer matrix, mixer milling process was applied. Wear, compression and three-point bending tests were conducted. It was observed that wear rate decreased by increasing in HA content in both atmosphere and artificial saliva. The results of compression tests showed that the addition of 2.5 percent HA to PMMA promoted ultimate compressive strength, yield strength and modulus while caused to decrease elongation at break. Also it was elucidated that addition of HA more than 2.5 wt.% caused a decrease in both ultimate compressive strength and compression yield strength and an increase in elongation at break. The results of three-point bending tests on the PMMA cements containing 2.5 percent HA demonstrated the maximum bending strength value and modulus among all the HA containing formulations. However there was no direct proportionality between the results of bending tests and the HA content and the addition of HA to PMMA (up to 10 wt.%) did not change the bending properties significantly.
Double-Lepton Polarization Asymmetries in $B_s \rar \phi \ell^+ \ell^-$ Decay in the Fourth-Generation Standard Model
Zebarjad, S. M.;Falahati, F.;Mehranfar, H.
High Energy Physics - Phenomenology , 2008, DOI: 10.1103/PhysRevD.79.075006
Abstract: In this paper, we investigate the effects of the fourth generation of quarks on the double-lepton polarization asymmetries in the $B_s \rar \phi \ell^+ \ell^-$ decay. It is shown that these asymmetries in $B_s \rar \phi \ell^+ \ell^-$ decay compared with those of $B \rar K \ell^+ \ell^-$ decay are more sensitive to the fourth-generation parameters. We conclude that an efficient way to establish the existence of the fourth generation of quarks could be the study of these asymmetries in the $B_s \rar \phi \ell^+ \ell^-$ decay.
Tensile properties of orthodontic elastomeric ligatures
Ahrari F,Jalaly T,Zebarjad M
Indian Journal of Dental Research , 2010,
Abstract: Context: Tensile properties of elastomeric ligatures become important when efficiency of orthodontic appliances is considered. Aims: The aim of this study was to compare tensile strength, extension to tensile strength, toughness and modulus of elasticity of elastomeric ligatures in both the as-received condition and after 28 days of immersion in the simulated oral environment. Furthermore, the changes that occurred in tensile properties of each brand of ligatures after 28 days were evaluated. Setting and Design : Experimental-laboratory based. Materials and Methods: Elastomeric ligatures were obtained from different companies and their tensile properties were measured using Zwick testing machine in both the as-received condition and after 28 days of immersion in the simulated oral environment. Statistical Analysis Used: The data were analyzed using independent sample t-tests, analysis of variance and Tukey tests. Results: After 28 days, all the ligatures experienced a significant decrease in tensile strength, extension to tensile strength and toughness ( P < 0.05), whereas modulus of elasticity increased in some groups and decreased in others. There were significant differences in tensile properties of different brands of ligatures in both conditions ( P < 0.05), with the exception of modulus of elasticity after 28 days. Conclusions : The decrease in strength properties of elastomeric ligatures shows that they should be replaced at each appointment to reduce the risk of rupture. There are significant differences in tensile properties of different brands of ligatures, which should be considered during selection of these products.
Soliton Decay in Coupled System of Scalar Fields
N. Riazi,A. Azizi,S. M. Zebarjad
Physics , 2002, DOI: 10.1103/PhysRevD.66.065003
Abstract: A system of coupled scalar fields is introduced which possesses a spectrum of massive single-soliton solutions. Some of these solutions are unstable and decay into lower mass stable solitons. Some properties of the solutions are obtained using general principles including conservations of energy and topological charges. Rest energies are calculated via a variational scheme, and the dynamics of the coupled fields are obtained by solving the field equations numerically.
A new approach for the analysis of functionally graded beams
M. Mirzababaee,M. Tahani,S.M. Zebarjad
Journal of Achievements in Materials and Manufacturing Engineering , 2006,
Abstract: Purpose: It is the intention of the present study to develope a new beam theory for the analysis of functionallygraded compopsite beams to overcome the shortcomings present in the existing beam theories.Design/methodology/approach: Within the displacement field of a first-order shear deformation theory and byusing the Hamilton principle the governing equations of motion are obtained for both the new and the existingbeam theories. The beams are assumed to have isotropic, two-constituent material distribution through thethickness.Findings: It is found that the procedure used is simple and straightforward and similar to the one used in thedevelopment of shear deformation plate and shell theories. It is analytically showed that the new approach yieldsidentical results as those obtained by using the existing first-order shear deformation theory.Research limitations/implications: The new approach can be adopted in developing higher-order sheardeformation and layerwise theories. It is believed that the new approach has advantage with respect to theexisting beam theories especially for developing beam layerwise theories.Practical implications: The new shear deformation beam theory can be used to develop a new beam elementfor analysis of practical composite beam structures.Originality/value: The paper introduces an approach to develop a new theory for modeling composite beams.The resulting equations of motion may be solved analytically or by using finite element method.
Influence of Nanosized Silicon Carbide on Dimensional Stability of Al/SiC Nanocomposite
S. M. Zebarjad,S. A. Sajjadi,E. Z. Vahid Karimi
Advances in Materials Science and Engineering , 2008, DOI: 10.1155/2008/835746
Abstract: This study concentrated on the role of particle size of silicon carbide (SiC) on dimensional stability of aluminum. Three kinds of Al/SiC composite reinforced with different SiC particle sizes (25 m, 5 m, and 70 nm) were produced using a high-energy ball mill. The standard samples were fabricated using powder metallurgy method. The samples were heated from room temperature up to 500∘C in a dilatometer at different heating rates, that is, 10, 30, 40, and 60∘C/min. The results showed that for all materials, there was an increase in length change as temperature increased and the temperature sensitivity of aluminum decreased in the presence of both micro- and nanosized silicon carbide. At the same condition, dimensional stability of Al/SiC nanocomposite was better than conventional Al/SiC composites.
The Effects of Fourth Generation on the double Lepton Polarization in B \rar K \ell^+ \ell^- decay
Bashiry, V.;Zebarjad, S. M.;Falahati, F.;Azizi, K.
High Energy Physics - Phenomenology , 2007, DOI: 10.1088/0954-3899/35/6/065005
Abstract: This study investigates the influence of the fourth generation quarks on the double lepton polarizations in B \rar K \ell^+ \ell^- decay. Taking |V_{t's}V_{t'b}|\sim \{0.01-0.03\} with phase about 100^\circ, which is consistent with the b\to s\ell^+\ell^- rate and the B_s mixing parameter Delta m_{B_s}$, we obtain that the double lepton(muon and tau) polarizations are quite sensitive to the existence of fourth generation. It can serve as a good tool to search for new physics effects, precisely, to indirect search for the fourth generation quarks(t', b').
Effect of temperature on tensile fracture mechanisms of a Ni-base superalloy
S.A. Sajjadi,S.M. Zebarjad
Archives of Materials Science and Engineering , 2007,
Abstract: Purpose: The Ni-base superalloy GTD-111 is used in manufacturing of the first stage blades of powerful gas turbines (over 125MW). The alloy posses appropriate microstructure and high temperature properties through precipitation hardening heat treatment. Among the properties, tensile properties of the alloy have strong influence on stability and life of the blades.Design/methodology/approach: Tensile tests over a wide range of temperatures from 25 to 950°C with a constant strain rate of 10-4s-1 were performed to study the tensile fracture mechanisms of the cast and heat treated superalloy. Scanning electron microscopy was used to provide structural and fractography evidence of the superalloy GTD-111at different temperatures.Findings: The fractography results of the tensile tested specimens were in good agreement with the variation in alloy ductility. Many fractography features such as: transgranular and intergranular fracture with fine dimples, cleavage facets and a combination of them were observed in the specimens tested at different temperatures.Research limitations/implications: Because fatigue is an important fracture mechanism at the service condition of the alloy it is suggested for future research to work on the simultaneous effects of tension and fatigue on the fracture mechanisms although, tensile properties alone are important for the alloy.Originality/value: It was found that different fracture mechanisms operated in different temperature ranges for example, while transgranular dimple fracture was dominant at 650°C, the dominant fracture mechanism at room temperature was intergranular.
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